Conventional oil and gas drilling techniques produce economical quantities of hydrocarbons when performed on porous formations. Often when a wellbore penetrates a porous formation, oil and gas flow into the low pressure region created by the wellbore. However, less porous, or impermeable, formations containing hydrocarbons are typically inaccessible using conventional methods. Because oil and gas cannot easily flow through impermeable formations in economic quantities, such impermeable formations cannot usually be drilled economically using only conventional drilling techniques.
Methods of hydraulic fracturing developed in previous decades allow impermeable formations to produce oil and gas in economic quantities. Generally, hydraulic fracturing methods pump a fluid into a formation at a pressure sufficient to cause the formation to fracture, thereby creating primary fractures. The primary fractures in the formation increase the effective porosity of the formation and allow for the economic production of hydrocarbons. The primary fractures typically extend orthogonally outward from the wellbore.
Due to the comparative inability of oil and gas to flow through impermeable formations, usually only those portions of the formations close to the wellbore or the primary fractures are in fluid communication with the wellbore. Consequently, even with primary fractures, there can remain large portions of the formation, even relatively close to the wellbore, that are not in fluid communication with the wellbore.